This invention relates to a discharge lamp lighting device for lighting a discharge lamp, and a projector device.
Discharge lamps are currently used in various fields, for example, as a light source of an LCD projector device or the like. In a conventional current control method at the time of lighting such a discharge lamp, immediately after ignition when a lamp lighting switch is turned on, the current is fixed at a magnitude approximately 1.5 to 2 times the magnitude of the steady-state current of the discharge lamp, and after the lapse of a predetermined time, that is, when the discharge state of the discharge lamp is stabilized and the voltage of the discharge lamp is raised to a predetermined level, the current is reduced and the steady-state current is gradually restored.
However, in the current control method as described above, since a large current which is greater than the steady-state current flows through the discharge lamp every time the discharge lamp is lit, the electrodes of the discharge lamp are quickly exhausted, shortening the lifetime of the discharge lamp.
To prevent the shortening of the lifetime of the discharge lamp, the electrodes of the discharge lamp must be less exhausted. For this, the preset value at which the current is fixed after ignition may be lowered.
However, the larger quantity of current is supplied to the discharge lamp, the faster the discharge state of the discharge lamp is stabilized. Therefore, if the preset value at which the current is fixed after ignition is lowered, the rise in voltage of the discharge lamp becomes too slow and it takes long to stabilize the discharge lamp.
It may be considered to dividedly control the current on several stages after ignition. In this case, however, the current control circuit is complicated, increasing the cost of discharge lamp lighting device rises and lowering its reliability.
Thus, a discharge lamp lighting device which is inexpensive and highly reliable and enables a longer lifetime of a discharge lamp has not been realized yet.
In view of the foregoing status of the art, it is an object of the present invention to provide a discharge lamp lighting device which is inexpensive and highly reliable and enables a longer lifetime of a discharge lamp, and a projector device.
In order to achieve the above-described object, a discharge lamp lighting device for lighting a discharge lamp according to the present invention comprises: starting means for applying a starting voltage to the discharge lamp at the time of starting and thus lighting the discharge lamp; voltage detection means for detecting a voltage of the discharge lamp; and current control means for controlling a current supplied to the discharge lamp on the basis of the result of detection at the voltage detection means; wherein the current control means, after ignition, starts controlling the current supplied to the discharge lamp on the basis of the result of detection at the voltage detection means and continuously increases the current supplied to the discharge lamp at a predetermined rate of increase to a predetermined current value larger than a steady-state current of the discharge lamp.
The discharge lamp lighting device according to the present invention constituted as described above has the current control means for controlling a current supplied to the discharge lamp on the basis of the result of detection at the voltage detection means, and this control means performs control to continuously change the quantity of current supplied to the discharge lamp after ignition at a predetermined rate of increase to a predetermined current value larger than a steady-state current of the discharge lamp on the basis of the result of detection of the voltage of the discharge lamp.
That is, in this discharge lamp lighting device, after ignition when lighting the discharge lamp, the quantity of current is continuously changed at a predetermined rate of increase to a predetermined current value larger than a steady-state current of the discharge lamp and the current is thus supplied to the discharge lamp.
To this end, voltage correction setting means for correcting the result of detection from the voltage detection means is provided in the current control means so that the current supplied to the discharge lamp is controlled on the basis of the detected voltage corrected by this voltage correction setting means. This voltage correction setting means performs correction to continuously decrease the detected voltage after the ignition at a predetermined rate of decrease from a predetermined voltage value, thus enabling continuous change in the current supplied to the discharge lamp at a predetermined rate of increase.
Moreover, power setting control means for controlling a target power value of power setting means which controls the current supplied to the discharge lamp is provided in the current control means. This power setting control means performs control to continuously increase the target power value after the ignition at a predetermined rate of increase, thus enabling continuous change in the current supplied to the discharge lamp at a predetermined rate of increase.
In this discharge lamp lighting device, by thus controlling the quantity of current, the time during which a large current larger than the steady-state current flows through the discharge lamp is significantly reduced, compared with the conventional discharge lamp lighting device.
Moreover, in this discharge lamp lighting device, by thus controlling the quantity of current, the current supplied to the discharge lamp is gradually increased and therefore the electrodes of the discharge lamp are gradually warmed up. As a result, heat load on the electrodes is reduced and thermal fatigue of the electrodes is reduced, thus restraining the exhaustion of the electrodes.
Furthermore, a projector device which projects light emitted from a discharge lamp to outside can be constituted by using the discharge lamp lighting device as described above. This projector device may be a projector device which modulates light emitted from the discharge lamp on the basis of an inputted image signal and emits the modulated light.
Also in the case of the projector device, similar to the discharge lamp lighting device, since the time during which a large current larger than the steady-state current flows through the discharge lamp is significantly reduced and the current supplied to the discharge lamp is gradually increased, the electrodes of the discharge lamp are gradually warmed up. Therefore, heat load on the electrodes is reduced and thermal fatigue of the electrodes is reduced, thus restraining the exhaustion of the electrodes.